Sprockets incorporating metal cushion rings have been used in automotive engine roller chain drive systems such as camshaft and balance shaft drives. The purpose of the cushion rings is to buffer or soften the roller-sprocket collision at the onset of meshing, thereby acting to reduce the chain meshing noise levels associated with roller chain drive systems. Roller-sprocket impact at the onset of meshing is the dominant noise source associated with roller chain drive systems and it occurs when a chain link leaves the span and its meshing roller collides with the sprocket tooth at engagement. It is believed that multiple roller-sprocket tooth impacts occur during the meshing phenomena and these impacts contribute to the undesirable noise levels associated with roller chain drives. There will be at least two impacts at the onset of meshing, a radial impact as the roller collides with the root surface and a tangential impact as the roller moves into driving position. It is believed that radial impact(s) will occur first, followed closely by tangential impact(s).
FIGS. 1 and 1A illustrate a conventional roller chain drive system 10 which is comprised of a cushion ring sprocket assembly 15, a roller chain 40, and at least one other sprocket (not shown). The roller chain 40 is conventional and includes a plurality of roller link assemblies, each comprising a pair of spaced-apart rollers 50 (i.e., rollers 50a, 50b, 50c, etc.) captured between a pair of parallel roller link plates 46, and the roller link assemblies are interconnected to each other in an endless fashion by pin link plates 48 located on opposite sides of the roller link assemblies. Each roller 50 is rotatably supported on a bushing (not shown) that spans the space between the roller link plates 46 and that is press-fit at its opposite ends into aligned apertures respectively defined in the roller link plates 46. The term “roller” as used herein is intended to encompass any rotating or non-rotating component located between the roller link plates 46 and intended to drivingly engage the sprocket 20, e.g., a roller supported on a bushing or a non-rotating bushing alone, without any rolling member supported thereon (also referred to in the art as a “bush chain”). Pins 42 are located in aligned apertures in the pin link plates 48 and roller link assemblies to pivotally interconnect the roller link assemblies. Each aligned pair of roller link plates 46 and the rollers 50 located therebetween defines a “roller link assembly” and is sometimes referred to herein as a “roller link row 45.” Each aligned pair of pin link plates 48 defines a “pin link row 47.” The chain link plates 46, 48 define a link plate height HP between upper and lower link edges E1, E2. The rollers 50 are centered halfway between the link plate edges E1, E2.
With reference also to FIG. 1B, the relevant components and features of a conventional cushion ring sprocket assembly 15 include a sprocket body 20 defined as a one-piece or multi-piece construction from steel or the like and having a full-circle complement of symmetrical sprocket teeth 22 manufactured according to an ISO 606:2004(E) standard or other symmetrical standard tooth forms as are typically used for automotive roller chain sprockets, first and second sprocket hubs 25a, 25b (that are part of the body 20) extending axially from the opposite first and second axial tooth faces/walls 21a, 21b, cushion rings 30 eccentrically mounted on the respective first and second hubs 25a, 25b, and circlip-type rings 32 or other means (not shown in FIG. 1 for clarity) to axially retain the cushion rings. A central bore or other recess B (also not shown in FIG. 1 for clarity) is defined in the sprocket body 20 and is adapted to receive a shaft or other rotating member that drives or that is driven by the sprocket body 20. The sprocket body 20 rotates about an axis of rotation L. The cushion ring 30 shown in FIG. 1 is in its free circular state, but there will be a combination of ring “lift” and “deflection” in normal engine operation as a function of chain tension and strand dynamics. “Lift” is defined as the distance that a cushion ring will lift or displace the next-meshing link row from its normal path during meshing and it effectively serves to lessen the effect of chordal action (see FIG. 2C); “deflection” is defined as deformation or ovalization of the cushion rings 30 under the force of chain tension.
FIG. 1A is a section view that illustrates the relationship of the meshing roller link row 45d, to the cushion rings 30 with the roller link plates 46 of roller link row 45d shown to be in hard contact with—and deflecting—the cushion rings. With a conventional system 10, the roller 50 is in hard root contact with the root surface 24 defined between successive sprocket teeth 22 as shown at RC, i.e., the cushion rings 30 can be deflected sufficiently to allow a roller 50 to make radial contact with the root surface 24 defined between successive sprocket teeth 22.
It is important to note that the chain link pitch P for a minimum as-manufactured roller chain 40 will be equal to the chordal pitch P for a roller chain sprocket 20 having a maximum as-manufactured tooth form. As is well known in the art, this equality for chain pitch P and sprocket chordal pitch P exists only at the aforementioned limits of the manufacturing tolerance range, and as the relevant chain and sprocket tolerances vary toward the opposite end of their respective manufacturing limits, there will be a pitch mismatch between chain link pitch which is more specifically designated PC and sprocket chordal pitch which is more specifically designated PS, with PC>PS. In other words, chain link pitch PC will always be greater than sprocket chordal pitch PS except at the specified manufacturing tolerance limit as noted. For the purpose of the included figures, chain link pitch is equal to sprocket chordal pitch, and accordingly, all rollers in the wrap angle θ for the conventional cushion ring sprockets will contact the root surface 24 of sprocket teeth 22 at the root diameter RD (see FIG. 2A) and the roller centers will be on the theoretical pitch diameter PD. It should be noted, however, that the tangential impact as the meshing roller moves into driving position, although still occurring on the root radius for the indicated build stack condition, will occur slightly radially outward of the root diameter toward the engaging flank.
As shown in FIG. 1 and more clearly in FIG. 2A, a greatly enlarged view of FIG. 1, a roller 50a is at a 12 o'clock position and roller 50b of roller link row 45d is the next roller to mesh with the sprocket 20. FIGS. 2A-2C illustrate the progression of roller link assembly row 45d in the chain free span as sprocket 20 rotates in a clockwise direction until roller 50b as shown in FIG. 2C is at the instant of radial meshing impact IR. The roller link plates 46 of roller link row 45d must deflect cushion rings 30 a distance L1 in order for the roller 50b to make radial meshing impact IR with the root surface 24.
Referring now to FIG. 3, a larger view of the FIG. 2C sprocket rotation, ring deflection L1 at the entry and L2 at the exit of wrap angle θ will be substantially equal. Also, there will be a clearance 55 defined between the inside edges of pin link plates 48 of pin link row 47a and the cushion rings 30 in the area of mid-wrap 35 where the cushion rings 30 are shown to be in hard contact with the hub surfaces 25a, 25b. The inside diameter of cushion rings 30 is larger than the outside diameters of hubs 25a, 25b, and noise attenuation is achieved as a function of the aforementioned ring deflection during meshing, with the rings 30 absorbing a portion of the meshing impact energy as the rings are deformed from their circular shape, as illustrated by the deflections L1 and L2 in FIG. 3. Accordingly, the inner edges of the chain link plates 46, 48 will be in hard contact with the cushion rings 30 for one or more link rows 45, 47 at the entry and the exit portions of the wrap angle θ, as shown, but the inner edges of the chain link plates 46, 48 do not contact the rings 30 through the entire wrap angle θ (as indicated by the space 55 in FIG. 3). The metal cushion rings 30 must be compressed a distance L1 in order for the rollers 50a, 50b to achieve initial radial meshing impact IR and continued roller-root surface contact RC, and the component geometry will permit this roller-to-root surface contact.
This initial radial meshing impact IR is normally the major contributor to the overall chain drive noise level, and the utilization of a conventional metal cushion ring sprocket notwithstanding, radial meshing impacts will still occur—albeit reduced impacts—along with the corresponding objectionable noise levels associated with roller-sprocket meshing impacts. Accordingly, it has been deemed desirable to develop a new and improved cushion ring sprocket to further reduce the noise levels associated with roller chain drives.